Dredging method



March 28, 1967 J. BALI. 3,310,894

DREDGING METHOD Filed May 11, 1964 2 Sheets-Sheet 1 JAMES BALL ATTORNEYS I N VEN TOR.

March 28, 1967 J BALL 3,310,894

' DREDGING METHOD Filed May 11, 1964' 2 Sheets-Sheet z INVENTOR. JAM E 5 BALL ATTORNEYS United States Patent 3,310,894 DREDGENG METHQD James Ball, Box 14, Nohleton, Ontario, Canada Fiied May 11, 1964, Ser. No. 366,262 3 Claims. (Cl. 37-195) This invention relates to a hydraulic dredging method and in particular to a method adapted to elevate solid particulate material from the floor of a deep body of water.

Since approximately the year 1870 it has been known that the floor of the sea is, in many areas, covered with a relatively dense scattering of mineral noduies which are exceptionally rich in manganese oxide and which contain'substantial amounts of other metals, chiefly iron, copper, cobalt and nickel. Formidable difliculties lie in the way of the economic recovery of these mineral nodules since the heaviest concentrations of the most valuable nodules lie, by and large, in ocean waters which might average 14,000 feet in depth.

These nodules were first discovered by a British oceanographic vessel which dredged them up from the bottom. However, to simply dredge these nodules from the bottom with a mechanical scoop or bucket would be quite impractical since the length of time taken to raise the full bucket to the surface, empty it and re turn the empty bucket to the floor of the sea would, in very deep water, make the rate of recovery quite uneconomical.

To recover the nodules by a kind of underwater hydraulic vacuum cleaner operated by conventional pumps presents very serious problems as well. It does not appear to be practical to construct such a device operated by suction pumps carried by a surface work station or ship and for obvious reasons the location of pumps adjacent the floor of the sea in depths averaging about 14,000 feet is undesirable.

It is the object of the present invention to provide a method of recovering or elevating these nodules from very deep water (of the order of 14,000 feet) which overcomes many of the heretofore insurmountable problems and which is simple in operation and which requires uncomplicated structure and apparatus in its function.

It will be apparent that the terms simple and uncomplicated are relative terms and that in practice many problems may arise that are neither simple nor uncomplicatedin their solution. It will also be apparent however, that the essence of the invention described and claimed herein is in fact simple and uncomplicated and that this simplicity isdirectly responsible for the fact that those particularly diflicult problems which have prevented the development of a practical method of recovering mineral nodules from very deep water have been avoided by the present invention.

In its essentials, the method of the present invention comprises the steps of traversing the floor of the body of water with an intake of a duct extending between the floor and a work station on the surface of the bodv of water, causing a sufflcient upward flow of water in the duct to deliver solid particulate material entrained therein to the work station by continuously injecting a substantially incompressible liquid having a density less than 1 into the duct adjacent its lower end to form a water/liquid mixture within the duct, the mixture having a density less than 1, separating the solid particulate material from the water/liquid mixture arriving at the work station, separating the liquid from the water/liquid mixture, discarding the water and re-injeeting the liquid into the duct adjacent its lower end to maintain the upward flow in the duct.

This method may be carried out by apparatus which 3,31,89 i Patented Mar. 28, 1&6?

is schematically illustrated in the accompanying drawings in which like reference numerals denote like parts in the various views and in which:

FIGURE 1 is a pictorial view of the entire apparatus used to practice the method of the present invention;

FlGURE 2 is a diagrammatic view of the apparatus located upon the surface work station or ship; and

FIGURE 3 is a perspective view of the apparatus located at the lower end of the duct.

. Referring now to the drawings and, in particular, to FIGURE 1 the floor 10 of the sea is shown to be littered with a plurality of mineral nodules 11 which it is desired to recover and to elevate to the work station constituted by the ship 12 lying upon the surface 13 of the sea. The recovery of these nodules is achieved by providing a duct 14 which extends between the floor 10 of the sea and the ship 12. Both the ship 12 and the recovery duct 14 are moved horizontally by means of a towing vessel 15 so that the lower intake end of the duct 14 may traverse the sea floor. The vessel 15 is joined by a plurality of towing cables 16 both to the ship 12 and to a plurality of spaced points along the length of the recovery duct 14. The number of cables used and the number of points at which these cables are secured to the duct 14 will vary within certain limits depending, among other things, upon the depth of water in which the duct is operating, the currents which exist and the nature of the duct construction itself.

In general, it is only essential that the towing ship 15 be capable of causing the lower intake end of the duct 14 to traverse the sea floor while, at the same time, maintaining the remainder of the duct 14 in a substantially upright position leading to the surface vessel or work station 12 without imparting such stresses upon the duct as would cause it to break.

The upper end of the duct 14 will be suitably supported adjacent the surface work station 12 and will be formed so as to discharge into the ship. Conveniently, the upper end 1411 of the duct 14 will be supported by separate floatation means adjacent the ship 12 and these means will be adjustable by floatation tanks in order to enable the vertical position of the duct 14 to be varied so as to accommodate variations in the depth of the sea floor. Means will also be provided whereby the total length of the duct 14 can be changed by adding or subtracting sections in a manner which is known in the well drilling art.

At the lower end of the duct 14 there is provided a flexible joint 17 to which is connected a lower short duct section 18 which, by means of a further flexible connection 18A is secured to a dredge or scoop generally indicated by reference character 20. The intake 19 for the duct 14 is located at the flexible connection 18A and the function of the dredge 20 is to gather the scattered nodules 11 and to mechanically deliver them to the intake 19 from where they will be elevated to the surface by means of an upward flow of water induced in the duct 14 by a method to be described below.

The dredge 20 generally comprises a forward and upwardly curving grating section 21, a central collecting section 22 and a rearward sieve section 23. As the dredge 20 traverses the sea floor 10 in the direction of the arrow 24, the forward grating section 21 will prevent any nodules 11 which are of a size such tha they might either clog the duct 14 or might be too heavy to be raised by the flow of water within the duct from entering the inlet at the flexible connection 19. For example, the grating section 21 might comprise a series of parallel bars separated by a distance of approximately 9 inches which would, therefore, permit nodules of 9 inches or less in diameter to pass through onto the collecting section 22 but which would cause the dredge to ride up and over nodules or other debris of a size larger than 9 inches in diameter.

The collecting section 22 comprises a generally flat bed 25 from which there are a plurality of downwardly extending scoops 26 which, as they traverse the sea floor, will raise nodules and silt and other sea floor debris onto the upper surface of the collecting section 22. The forward passage of the dredge through the water will cause a relative flow of water across the upper surface of the collecting section 22 which will, in turn, cause the material lying upon its surface to move rearwardly relative to the dredge onto the sieve section 23. The sieve section 23 comprises a. grating which may be formed from parallel bars which are separated by a distance equal to the size of the smallest nodule which it is considered economical to raise to the surface. For example, these bars might be spaced by a distance of one inch and any material which is less than one inch in diameter will pass through the sieve and will be re-dcposited upon the sea floor in the path from which the nodules have been removed. This material Will not, therefore, be elevated to the surface through the duct 14 and, accordingly, the dredge 20 constitutes a preliminary separation of desired material from undesired material which takes place in a simple and uncomplicated manner on the sea floor and which delivers to the intake 19 at the flexible connection 13A of the duct 14 only that material which it is intended to raise to the surface.

Having now described the duct 14 and the method by which the intake of the duct 14 is fed with material it is desired to raise to the surface, the method of achieving the upward flow of water through the duct 14 will be described.

Running parallel to the duct 14 and secured thereto is a secondary conduit 27. Conveniently, both the duct 14 and the conduit 27 may be housed in a streamlined fairing or housing 27a as seen in FIGURE 1. The conduit 27, at its lower end, is in communication with the interior of a manifold or chamber 28 which surrounds the duct 14 adjacent its lower end. The duct 14, within the manifold 0r chamber 28 is provided with a plurality of ports or perforations 2 (see FIG. 3) so that the interior of the duct 14 is in communication with the interior of the manifold or chamber 28 which, in turn, is connected to the conduit 27.

The upper end of the conduit 27 is connected to the pressure or outlet port 30 of a high pressure, high capacity pump 31, the intake port 32 of which is connected to a supply of a substantially incompressible liquid having a density less than 1 contained in a supply tank 33.

In operation, the pump 31 is energized and the substantially incompressible liquid having a density less than 1 is pumped from the supply tank 33, down the conduit 27 into the chamber or manifold 28 where it is introduced through the ports 29 into the interior of the duct 14. In the duct 14 at the manifold or chamber 28, the low density liquid mixes with the sea water to form a water/ liquid mixture, the density of which is less than the density of the ambient sea water with the result that this sea water/liquid mixture rises within the duct 14. Preferably there will be a large number of perforations 2? so that the kerosene will be broken up and will intimately mix with the sea water in the duct 14. Various perforation configurations and orientations may be used to achieve this end. The continuous introduction of the low density incompressible liquid through the port 29 will cause a continuous upward flow in the duct 14 which will, in turn, induce a flow into the inlet 19 of the duct 14 adjacent the flexible connection 18A. This flow at the inlet will carry with it entrained nodules from the sieve section 23 and these nodules will be raised through the duct 14 by the upward flow therein to the upper end 14a of the duct 14 Where the nodules will be discharged into the work station or ship 12.

Referring now to FIGURE 2, the work station is schematically illustrated as being carried by the ship 12 into which the upper end 14a of the duct 14 discharges. The upper end 14a of the duct 14 is curved at 34 to discharge the water/liquid/nodule mixture onto the surface of a sloping screen 35 which permits the water/liquid mixture to fall through as indicated at 36 onto a collection surface 37 having an aperture 38 through which the water/ liquid mixture passes into the tank 33. The nodules are moved along the sloping screen 35 by gravity or by agitation of the screen and are discharged into a collection bin 39 where they are stored until they may be further processed or transferred to barges or the like for transportation to shore.

In the tank 33 the sea water and low density liquid will separate due to their different densities with the low density liquid 40 floating on top of the sea water 41. From time to time valve 42 may be opened to discard sea water through duct 43 so as to maintain the interface 44 between the liquid and the sea water below the inlet 45 of the conduit 46 leading to the inlet 32 of the pump 31. From the supply tank 33, therefore, the low density liquid 40 which has been separated from the water/ liquid mixture arriving at the work station may now be pumped down the conduit 27 to be re-injected into the manifold or chamber 28 adjacent the lower end of the duct 14 in order to maintain the upward flow in the duct 14 so that the process described is continuous.

If, for any reason, it is necessary to interrupt the continuous process, means must be provided to enable those nodules entrained in the liquid in the duct 14 to escape since they would otherwise settle to the bottom of the duct 14 and would probably cause an obstruction which could not be cleared by normal operation of the system. These means are provided by a dump valve 47 located at a curved point 48 in the duct 14 below the manifold or chamber 28 :and above the flexible connection 17. This valve 47 is held lightly closed by a relatively weak spring 49, the valve also being held closed during the operation of the system by the relative under-pressure existing within the duct 14 in comparison with the ambient sea water. However, when the introduction of liquid is ceased in manifold 28, the pressure within the duct 14 will tend to equalize with the ambient sea water and, in addition, the nodules then settling down through the duct 14, falling upon the valve 47 would cause it to 'open and permit these nodules to fall free of the duct 14 onto the sea floor 19.

The substantially incompressible liquid of a density less than that of water or sea water which is considered to be most practical is kerosene. Kerosene has a density of approximately 0.80 compared to the average density of sea water which is 1.05. Kerosene is substantially incompressible and separates readily from sea water by differential floatation.

Calculations have been made which show that for a duct 14 having an inside diameter of 16 inches, a flow rate of 10 feet per second can be achieved by introducing substantially 50 to of this flow of kerosene into the duct 14 from the manifold 28 and that this flow will carry 20% by weight of nodules of the kind which this invention seeks to recover. These nodules have an average density of 2.4 and their settling rate is therefore significantly less than the flow rate of 5 to 10 feet per second and they can easily be raised by flows of this order of magnitude.

The kerosene pump 31 must be capable of delivering substantial volumes of kerosene (an amount equal to a flow rate 'of between 2 /2 and 5 feet per second in a 16 inch duct) at pressures of the order of 2,000 pounds per square inch in order to deliver the necessary volume of kerosene to the manifold 28 which will lie in very deep water adjacent the bottom of the duct. The pressures required will, of course, vary with the depths at which the manifold 28 is located but a pressure of approximately 2,030 pounds per square inch will be sufficient to deliver kerosene to the manifold 28 lying at a depth of approximately 15,000 feet in sea Water having an average density of 1.05.

Instead of kerosene, any other light hydrocarbon liquid might be used but kerosene appears to be the most practical liquid from the point of cost, safety, density, and ease of separation from water. Gasoline may be used if its inflammability is reduced or eliminated.

It is to be expected, 'of course, that the recovery of kerosene in the tank 33 will not be 100% eflicient. Make-up kerosene will need to be supplied since there will necessarily be losses arising out of separation techniques and leakages in both the conduit 27 and the duct 14. It is anticipated, however, that this make-up kerosene will not involve excessive amounts.

As was stated at the 'outset, the object of this invention is to provide a relatively simple and uncomplicated method of elevating mineral nodules from the floor of a very deep body of water. The simplicity of the invention, in its essentials, will be apparent from the preceding description and the operation of the method is quite uncomplicated. Obviously, problems relating to the support of the duct 14, its construction, details relating to traversing the sea floor and other problems will arise which may present ditficulties in solution but these are all ancillary to the present invention minor modifications of which are contemplated within the spirit of the invention and the scope of the appended claims.

What I claim as my invention is: 1. The method of recovering solid particulate material from the floor of a deep body of water comprising the steps of:

traversing the floor of the body of water with an intake of a duct extending between the floor and a work station 'on the surface of the body of water, causing a sufficient upward flow of water in the duct to deliver solid particulate material entrained therein to the work station by continuously introducing a substantially incompressible liquid having a density less than 1 into the duct adjacent its lower end to form a water/liquid mixture within the duct, said mixture having a density less than 1,

separating the solid particulate material from the water/ liquid mixture arriving at the work station,

separating the liquid from the Water/liquid mixture,

discarding the water,

re-introducing the liquid into the duct adjacent its lower end to maintain the upward flow in the duct.

2. The method of recovering solid particulate material from the floor of a deep body of water comprising the steps of:

traversing the floor with a scoop adapted to concentrate scattered solid particulate material in an intake of a duct extending between the floor and a work station on the surface of the body of water, causing a suificient upward flow of water in the duct to deliver solid particulate material entrained therein to the work station by continuously introducing a substantially incompressible liquid having a density less than 1 into the duct adjacent its lower end to form a water/liquid mixture within the duct, said mixture having a density less than 1,

separating the solid particulate material from the water/liquid mixture arriving at the work station,

separating the liquid from the water/liquid mixture,

discarding the water,

re-introducing the liquid into the duct adjacent its lower end to maintain the upward flow in the duct.

3. The method of recovering solid particulate material from the floor of a deep body of water comprising the steps of traversing the floor with a scoop adapted to concentrate scattered solid particulate material in an intake of a duct extending between the floor and a work station on the surface of the body of water,

causing a suflicient upward flow of water in the duct to deliver solid particulate material entrained therein to the work station by continuously introducing substantially incompressible kerosene having a density less than that of water into the duct adjacent its lower end to form a water/kerosene mixture within the duct, said mixture having a density less than 1, sepanating the solid particulate material from the water/ kerosene mixture arriving at the work station,

separating the kerosene from the water/kerosene mixture,

discarding the water,

re-introducting the kerosene into the duct adjacent its lower end to maintain the upward flow in the duct.

References Cited by the Examiner UNITED STATES PATENTS 80,225 7/1868 Robertson 3761 1,415,113 5/1922 Phillips 3761 X 2,144,743 1/1939 Schulz 3762 X 2,191,424 2/ 1940 Cardinal.

2,678,203 5/1954 Hufi 37-63 X 3,226,854 1/1966 Mero 3758 ABRAHAM G. STONE, Primary Examiner. I. R. OAKS, Assistant Examiner, 

1. THE METHOD OF RECOVERING SOLID PARTICULATE MATERIAL FROM THE FLOOR OF A DEEP BODY OF WATER COMPRISING THE STEPS OF: TRAVERSING THE FLOOR OF THE BODY OF WATER WITH AN INTAKE OF A DUCT EXTENDING BETWEEN THE FLOOR AND A WORK STATION ON THE SURFACE OF THE BODY OF WATER, CAUSING A SUFFICIENT UPWARD FLOW OF WATER IN THE DUCT TO DELIVER SOLID PARTICULATE MATERIAL ENTRAINED THEREIN TO THE WORK STATION BY CONTINUOUSLY INTRODUCING A SUBSTANTIALLY INCOMPRESSIBLE LIQUID HAVING A DENSITY LESS THAN 1 INTO THE DUCT ADJACENT ITS LOWER END TO FORM A WATER/LIQUID MIXTURE WITHIN THE DUCT, SAID MIXTURE HAVING A DENSITY LESS THAN 1, SEPARATING THE SOLID PARTICULATE MATERIAL FROM THE WATER/ LIQUID MIXTURE ARRIVING AT THE WORK STATION, SEPARATING THE LIQUID FROM THE WATER/LIQUID MIXTURE, DISCARDING THE WATER, RE-INTRODUCING THE LIQUID INTO THE DUCT ADJACENT ITS LOWER END TO MAINTAIN THE UPWARD FLOW IN THE DUCT. 